1. Field of the Invention
This invention relates to a method of recognizing the shape of a road which can be used by, for example, a system provided on a vehicle. In addition, this invention relates to an apparatus for recognizing the shape of a road which can be used by, for example, a system provided on a vehicle. Furthermore, this invention relates to a recording medium which stores a computer program for recognizing the shape of a road.
2. Description of the Related Art
A known obstacle detecting apparatus for a vehicle emits a forward wave beam such as a light beam or a millimeter wave beam from the body of the vehicle, and controls the forward wave beam to periodically scan a given angular region in front of the body of the vehicle. In the case where an obstacle exists in the given angular region, the forward wave beam encounters the obstacle before being at least partially reflected thereby. A portion of the reflected wave beam returns to the apparatus as an echo wave beam. The apparatus detects the obstacle in response to the echo wave beam.
The known obstacle detecting apparatus is used in a warning system for a vehicle which alarms when an obstacle such as a preceding vehicle exists in a given angular region in front of the present vehicle. The known obstacle detecting apparatus is used also in a system for a vehicle which controls the speed of the vehicle to maintain a proper distance between the vehicle and a preceding vehicle.
The known obstacle detecting apparatus additionally has the function of determining whether or not the detected obstacle is a preceding vehicle. In general, this determination is responsive to the output signals from a steering angle sensor and a yaw rate sensor. In the case where the present vehicle is traveling along a straight portion of a road while a preceding vehicle is traveling along a curved road portion extending ahead of the straight road portion, the known obstacle detecting apparatus has a chance of erroneously determining the preceding vehicle.
In view of such a problem in the known obstacle detecting apparatus, it is proposed to recognize the shape of a road from objects and delineators on the sides of the road.
Japanese patent application publication number 5-159199 discloses a warning system for a vehicle. The system in Japanese application 5-159199 emits a forward laser beam from the body of the vehicle, and controls the forward laser beam to periodically scan a given angular region in front of the body of the vehicle. In the case where an object exists in the given angular region, the forward laser beam encounters the object before being at least partially reflected thereby. A portion of the reflected laser beam returns to the system as an echo laser beam. The system detects the object in response to the echo laser beam. In addition, the system calculates the distance to the object from the time interval between the moment of emission of the forward laser beam and the moment of reception of the related echo laser beam. In the system of Japanese application 5-159199, a decision is made as to whether or not the distance to the object monotonically changes. When it is decided that the distance to the object monotonically changes, the object is judged to be a reflector on a curved road side. In this case, the system stops the generation of an alarm.
The system of Japanese application 5-159199 does not discriminate a reflector on a right-hand road side and a reflector on a left-hand road side from each other. Therefore, it is difficult for the system to distinctively recognize a right-hand road edge and a left-hand road edge.
Japanese patent application publication number 8-249598 discloses an apparatus for sensing delineators and recognizing a road shape from information about the sensed delineators. The apparatus in Japanese application 8-249598 emits a forward electromagnetic wave beam from the body of the vehicle, and controls the forward electromagnetic wave beam to periodically scan a given angular region in front of the body of the vehicle. In the case where an object exists in the given angular region, the forward electromagnetic wave beam encounters the object before being at least partially reflected thereby. A portion of the reflected electromagnetic wave beam returns to the apparatus as an echo electromagnetic wave beam. The apparatus detects the object in response to the echo electromagnetic wave beam. Specifically, the apparatus calculates the distance to the object from the time interval between the moment of emission of the forward electromagnetic wave beam and the moment of reception of the related echo electromagnetic wave beam. In addition, the apparatus calculates the direction of the object relative to the vehicle.
The apparatus in Japanese application 8-249598 decides whether each detected object is a delineator on a right-hand road side or a delineator on a left-hand road side in response to the horizontal variation in the position of the object relative to the vehicle. For example, decided delineators on a right-hand road side are linked by lines, and the set of the lines is recognized as a right-hand road edge. In the apparatus of Japanese application 8-249598, the decision as to whether each detected object is a right-hand delineator or a left-hand delineator is responsive to the horizontal variation in the relative position of the object. Therefore, it is difficult to implement the decision regarding an object detected for the first time. The result of the decision tends to be inaccurate when the horizontal variation in the relative position of an object is small or when the sign of the horizontal variation in the relative position of an object inverts.
Japanese patent application publication number 10-239436 discloses an apparatus for detecting the vehicle-to-vehicle distance. The apparatus in Japanese application 10-239436 emits a forward laser beam, and controls the forward laser beam to periodically scan a given angular region in front of the body of the present vehicle. The apparatus in Japanese application 10-239436 detects objects in the given angular range from return laser beams coming therefrom. Specifically, the apparatus detects the distances to the objects and the directions (the angular positions) of the objects relative to the present vehicle. The detected objects include reflectors on the right-hand and left-hand sides of the road. In the apparatus of Japanese application 10-239436, the shape of the road is recognized from the loci (trajectories) of detected reflectors on the road sides.
Japanese patent application publication number 7-270536 discloses an object determination apparatus for a vehicle. The apparatus in Japanese application 7-270536 emits a forward laser beam, and controls the forward laser beam to periodically scan a given angular region in front of the body of the present vehicle. The apparatus in Japanese application 7-270536 detects objects in the given angular range from return laser beams coming therefrom. Specifically, the apparatus detects the distances to the objects and the directions (the angular positions) of the objects relative to the present vehicle. The detected objects are sorted with respect to distance. Each continuity between two adjacent objects among the detected objects is judged, and the detected objects are separated into groups in response to the judgement results. According to the total number of the objects in each group and the relation among the relative positions thereof, it is decided whether they are discrete objects or continuous objects. The continuous objects are recognized as road facilities, while the discrete objects are recognized as preceding vehicles.
It is a first object of this invention to provide a method of accurately recognizing the shape of a road even when the time-domain variation in the relative position of a road-side object is unknown.
It is a second object of this invention to provide an apparatus for accurately recognizing the shape of a road even when the time-domain variation in the relative position of a road-side object is unknown.
It is a third object of this invention to provide a recording medium which stores a computer program for accurately recognizing the shape of a road even when the time-domain variation in the relative position of a road-side object is unknown.
A first aspect of this invention provides a method of applying a transmission wave to a predetermined angular range in a width-wise direction of a vehicle, and recognizing a shape of a road extending ahead of the vehicle on the basis of a reflected wave which results from reflection of the transmission wave. The method comprises the steps of generating object-unit data pieces containing at least data pieces representing distances to objects in correspondence with vehicle-width-wise direction angles on the basis of the reflected wave; determining whether each object is moving or stationary on the basis of a speed of the vehicle and a relative speed of the object which is derived from the reflected wave; extracting ones from the object-unit data pieces which are effective for road shape recognition on the basis of a result of determining whether each object is moving or stationary, and grouping ones of the extracted object-unit data pieces which represent monotonically increasing distances as viewed along one of clockwise and counterclockwise angle directions to generate data representing a road-side-object group; and recognizing a road edge on the basis of the data representing the road-side-object group.
A second aspect of this invention provides an apparatus for recognizing a road shape. The apparatus comprises radar means for applying a transmission wave to a predetermined angular range in a width-wise direction of a vehicle, and detecting each object on the basis of a reflected wave which results from reflection of the transmission wave; and recognizing means for recognizing a shape of a road extending ahead of the vehicle on the basis of a result of detection by the radar means. The recognizing means comprises 1) object-unit data generating means for generating object-unit data pieces containing at least data pieces representing distances to objects in correspondence with vehicle-width-wise direction angles on the basis of the result of the detection by the radar means; 2) object recognizing means for determining whether each object is moving or stationary on the basis of a speed of the vehicle and a relative speed of the object which is derived from the reflected wave; 3) effective data extracting means for extracting ones from the object-unit data pieces which are effective for road shape recognition on the basis of a result of the determination by the object recognizing means; 4) road-side-object group data generating means for grouping ones of the extracted effective object-unit data pieces which represent monotonically increasing distances as viewed along one of clockwise and counterclockwise angle directions to generate data representative of a road-side-object group; and 5) road edge recognizing means for recognizing a road edge on the basis of the data representative of the road-side-object group which are generated by the road-side-object group data generating means.
A third aspect of this invention is based on the second aspect thereof, and provides an apparatus wherein the road-side-object group data generating means comprising means for grouping ones of the extracted effective object-unit data pieces which represent monotonically increasing distances as viewed along the clockwise angle direction to generate data representative of a first road-side-object group, and means for grouping ones of the extracted effective object-unit data pieces which represent monotonically increasing distances as viewed along the counterclockwise angle direction to generate data representative of a second road-side-object group, and wherein the road edge recognizing means comprises means for recognizing a first road edge on the basis of the data representative of the first road-side-object group, and means for recognizing a second road edge on the basis of the data representative of the second road-side-object group.
A fourth aspect of this invention is based on the second aspect thereof, and provides an apparatus wherein the road-side-object group data generating means comprises means for grouping ones of the extracted effective object-unit data pieces which represent monotonically increasing distances as viewed along one of clockwise and counterclockwise angle directions, and which relate to conditions where a distance between neighboring objects is equal to or less than an adjacent-state-corresponding value to generate data representative of a road-side-object group.
A fifth aspect of this invention is based on the second aspect thereof, and provides an apparatus wherein the road edge recognizing means comprises means for recognizing a road edge on the basis of the data representative of the road-side-object group which has at least three object-unit data pieces.
A sixth aspect of this invention is based on the fifth aspect thereof, and provides an apparatus wherein the road edge recognizing means comprises means for forming lines connecting objects indicated by the object-unit data pieces in the road-side-object group through interpolation, and means for recognizing the road edge on the basis of the formed lines.
A seventh aspect of this invention is based on the sixth aspect thereof, and provides an apparatus wherein the road edge recognizing means comprises means for calculating a point of intersection between an extension of a set of the formed lines and an width-wise-direction axis of the vehicle, means for connecting the point of intersection and a nearest object by an additional line through interpolation, and means for recognizing a road edge extending from a place near the vehicle on the basis of the additional line and the set of the formed lines.
An eighth aspect of this invention is based on the second aspect thereof, and provides an apparatus wherein the object-unit data generating means comprises means for unifying ones of point-unit data pieces into segment data pieces, the point-unit data pieces representing distances and angles corresponding to point units for objects, the unified ones corresponding to point units close to each other in position and distance, and means for setting the segment data pieces as the object-unit data pieces.
A ninth aspect of this invention is based on the second aspect thereof, and provides an apparatus wherein the effective data extracting means comprises means for, to extract the effective object-unit data pieces, discarding ones among the object-unit data pieces which satisfy conditions as follows:
1) a shape of a related object is outside a predetermined range; and
2) a related object is located near a moving object.
A tenth aspect of this invention is based on the second aspect thereof, and provides an apparatus wherein the road-side-object group data generating means comprises means for determining whether or not a farthest object in the road-side-object group is on a road side same as a road side for other objects in the road-side-object group on the basis of a positional relation among the farthest object and the other objects, and means for keeping the farthest object in the road-side-object group only when the farthest object is on the same road side.
An eleventh aspect of this invention is based on the third aspect thereof, and provides an apparatus wherein the road-side-object group data generating means comprises means for determining whether or not a farthest object in the first road-side-object group and a farthest object in the second road-side-object group are a same, means for, when the farthest objects are the same, removing the farthest object from the first and second road-side-object groups and changing the first and second road-side-object groups into third and fourth road-side-object groups respectively, and means for generating data representative of the third road-side-object group and data representative of the fourth road-side-object group, and wherein the road edge recognizing means comprises means for recognizing the first road edge on the basis of the data representative of the third road-side-object group, and means for recognizing the second road edge on the basis of the data representative of the fourth road-side-object group.
A twelfth aspect of this invention is based on the third aspect thereof, and provides an apparatus wherein the road-side-object group data generating means comprises means for determining whether or not a farthest object in the first road-side-object group and a farthest object in the second road-side-object group are a same, means for, when the farthest objects are the same, determining which of the first and second road-side-object groups actually contains the farthest object at a higher possibility on the basis of positional relations among the farthest object and other objects in the first and second road-side-object group, means for keeping the farthest object in one of the first and second road-side-object groups which corresponds to the higher possibility and removing the farthest object from the other of the first and second road-side-object groups to generate third and fourth road-side-object groups from the first and second road-side-object groups respectively, and means for generating data representative of the third road-side-object group and data representative of the fourth road-side-object group, and wherein the road edge recognizing means comprises means for recognizing the first road edge on the basis of the data representative of the third road-side-object group, and means for recognizing the second road edge on the basis of the data representative of the fourth road-side-object group.
A thirteenth aspect of this invention is based on the second aspect thereof, and provides an apparatus wherein the road-side-object group data generating means comprises means for unconditionally removing a farthest object from the road-side-object group, and using a resultant road-side-object group as a final road-side-object group.
A fourteenth aspect of this invention provides a recording medium storing a program for controlling a computer operating as the recognizing means in the apparatus of the second aspect of this invention.
A fifteenth aspect of this invention provides an apparatus for a vehicle. The apparatus comprises first means for detecting stationary objects in an area extending ahead of the vehicle; second means for calculating angular positions of the stationary objects detected by the first means relative to the vehicle; third means for calculating distances to the stationary objects detected by the first means relative to the vehicle; fourth means for calculating distances between neighboring ones of the stationary objects detected by the first means; fifth means for sequentially arranging the stationary objects detected by the first means in an order of angular position; sixth means for selecting ones from among the stationary objects arranged by the fifth means, wherein the selected objects satisfy conditions that a distance to each selected object increases as the selected object changes from one to a next in the order of angular position, and that distances between neighboring ones of the selected objects are equal to or less than a predetermined reference value; seventh means for grouping the stationary objects selected by the sixth means into a group; and eighth means for recognizing a road edge in response to the group generated by the seventh means.